1. Field of the Invention
The present invention relates to a glazing comprising a sheet of glass with a member bonded to it by adhesive. More particularly the glazing may be for a vehicle window, and the member may be a plate, especially a mounting plate for an accessory or a piece of equipment which is ancillary to the window, e.g. a wiper assembly, lock or catch, or a support strut for an opening window.
2. Description of the Related Art
There has been a continuing increase over the years in the amount of equipment provided on vehicles, especially cars. Moreover, vehicle manufacturers have developed a preference for vehicle components to be supplied as major assemblies, incorporating several smaller components, as this facilitates assembly of the vehicle on the production line. Consequently, there is an increasing need for accessories or auxiliary equipment to be attached to glass sheets (normally bent glass sheets which are either toughened or laminated), and there is also a consequent need for provision for such attachment to be included as part of the glazing as supplied to the vehicle manufacturer.
It is known from EP 368 728 to bond a plate to a sheet of glass with adhesive, wherein the entire surface of the plate is coated with adhesive, and holes are provided in the glass to increase the surface area of glass covered by adhesive, and to provide a mechanical key for the adhesive. However, the drilling of holes in glass is both time consuming and expensive; it requires extra equipment to be provided in the glass processing line to perform the drilling, reduces production rates, and the holes weaken the glass. For these reasons it is generally desirable to minimise the number of holes that need to be drilled in a glazing, and indeed it is preferable to avoid the need for holes altogether.
It is of course possible to bond items to the surface of a glass sheet without the attendant provision of one or more holes, but there are strict limits on the size of the item that may be thus bonded, and the weight or applied force which the adhesive bond can withstand. When it is desired to bond a larger item to glass, or to accommodate a larger weight or force, it is not satisfactory simply to increase the area over which adhesive is applied, for a variety of problems may be encountered.
For instance, when a structural adhesive is employed, i.e. a rigid, non-elastic, adhesive, it is found that as the area of adhesive increases in size, there is an increased tendency for the glass to break, or for damage to occur to the plate being bonded. This results from the differing coefficients of thermal expansion of glass and the material of which the plate is composed, which results in the generation of stresses when the glazing is subjected to variations in temperature. While elastic adhesives are able to accommodate a certain degree of differential thermal expansion owing to their flexibility, the very fact that they flex means that they are not suitable for applications where there is a tight tolerance on the positioning of the item to be bonded, or where the item is to be mounted in a rigid and immobile fashion.
EP 532 384 discloses an arrangement for mounting a wiper on an automotive window, which is susceptible to the problems outlined above. A support plate is bonded to the window with a layer of adhesive, and a driving mechanism is attached to the plate by fixings such as bolts or screws. The adhesive may be an epoxy resin, i.e. a structural adhesive.
It would be desirable to alleviate the problems associated with structural adhesives so as to be able to exploit their greater potential bond strength, and greater suitability for applications requiring a high degree of accuracy and positional certainty.
It has been unexpectedly found that the provision of multiple areas of adhesion, instead of one relatively large area, reduces the likelihood of breakage of the glass linked to the presence of the item bonded to the glass, and yields better overall performance.
According to the present invention there is provided a glazing comprising a glass sheet with a rigid member bonded to it by adhesive, wherein the adhesive is provided on at least two discrete areas of the member or glass sheet.
Preferably, the adhesive is a structural adhesive, i.e. one that is rigid, inelastic and non-deformable when set. Structural adhesives are capable of bearing loads of great magnitude, which may be greater than the weight of the bonded parts.
Generally, the material of which the rigid member is composed (normally metal) has a different coefficient of thermal expansion from the glass to which it is bonded. The member may be formed from a single element such as a single piece of metal, or it may comprise a number of elements which are united so as to behave as a single rigid element, i.e. the member is unitary in nature, even when made from a plurality of components.
It is also preferable for the areas of adhesive to be selected such that they are on opposite sides of the overall centre of gravity of the member together with any item attached to the member. The moment of force which the weight of the member and any attached item exerts on the adhesion points is thereby minimised. Preferably the adhesive is the sole means of attaching the rigid member to the glazing, i.e. it is not supplemented by mechanical fixings.
The invention also provides a method of bonding a rigid member to a glazing by adhesive, the glazing comprising a glass sheet, wherein the method includes the steps of:
a) applying adhesive to at least two discrete areas of the member or glass sheet,
b) positioning the member relative to the glass sheet,
c) pressing the member and glass sheet together so that the adhesive is in intimate contact with both member and glass sheet.